Senior Backend Engineer

Phonely; San Francisco (CA); On-site; USD 140,000 - 190,000; Full time

Job summary

Phonely in San Francisco is seeking a Senior Backend Engineer (Python) to build and maintain stateful Python systems that drive the voice AI in real-time conversations. You will integrate multiple LLM providers, design robust APIs, and write high-performance code.

This role focuses on testing, reliability, and scalable architectures, with emphasis on security, metrics, and observability. Office-based 5 days a week in San Francisco offers a collaborative, fast-moving environment shaping

Qualifications

• 5+ years writing Python, experience writing async web apps using FastAPI, testing frameworks.
• Understanding of LLMs, APIs, cloud and CI/CD pipelines.
• Comfortable with technical specifications.
• Understanding of good architecture and security practices.
• Strong technical and communication skills.
• Experience with AWS and Kubernetes.

Responsibilities

• Build and maintain Python-based state systems that drive what the voice AI says and does across complex, real-time conversations.
• Integrate and orchestrate multiple LLM providers, including prompt design, tool/function calling, routing, and fallbacks.
• Write clean, maintainable, high-performance Python code, leveraging asyncio, OOP, and best practices.
• Write automated tests and validation suites to ensure correctness, resilience, and safe iteration of agent logic and state transitions.
• Monitor production systems, debug agent behavior, and continuously improve reliability and conversation quality.
• Implement comprehensive metrics, logging, and alerting to validate correctness, detect failures early, and maintain extremely high availability.
• Design database schemas, optimize queries, and operate both SQL and NoSQL databases in production.
• Build and operate authentication and authorization mechanisms with strong security guarantees.
• Design and build microservices-based architectures.

Skills

Python

Async web apps (FastAPI)

LLMs & APIs

CI/CD pipelines

Security & architecture

AWS

Kubernetes

Testing frameworks

Communication skills

Tools

FastAPI

Docker

Redis

Job description

Senior Backend Engineer (Python)

At some point in the future, every business will answer their phone with voice AI. We are making sure that when they build that AI agent, the experience of doing so doesn’t suck. We’re growing incredibly fast and need someone who thrives in a dynamic, high‑pressure environment. This role is critical to the success of our company and expects a highly technical, driven, and fun collaborator who will roll up their sleeves, dig in, and double down when things get tough.

This is an engineer’s role: you will be writing code a lot of the time. If you’re looking for a cushy corporate job where nothing gets done, you may prefer another company. If you want to be part of a winning team and make a real difference, read on. This role is in an office 5 days a week in San Francisco.

Your day to day

• Build and maintain Python-based state systems that drive what the voice AI says and does across complex, real‑time conversations.

• Integrate and orchestrate multiple LLM providers, including prompt design, tool/function calling, routing, and fallbacks.

• Write clean, maintainable, high-performance Python code, leveraging asyncio, OOP, and best practices.

• Write automated tests and validation suites to ensure correctness, resilience, and safe iteration of agent logic and state transitions.

• Monitor production systems, debug agent behavior, and continuously improve reliability and conversation quality.

• Implement comprehensive metrics, logging, and alerting to validate correctness, detect failures early, and maintain extremely high availability.

• Design database schemas, optimize queries, and operate both SQL and NoSQL databases in production.

• Build and operate authentication and authorization mechanisms with strong security guarantees.

• Design and build microservices-based architectures.

Qualifications

• 5+ years writing Python, experience writing async web apps using FastAPI, testing frameworks.

• Understanding of LLMs, APIs, cloud and CI/CD pipelines.

• Comfortable with technical specifications.

• Understanding of good architecture and security practices.

• Strong technical and communication skills.

• Experience with AWS and Kubernetes.

Our Software Stack

• Backend: Python, microservices, async programming

• Cloud & Infrastructure: AWS, GCP, Kubernetes, Redis

• Databases: Firebase, Supabase

• Frontend: Next.js

• Observability & Monitoring: Datadog, logging, metrics, tracing

• Telephony & Voice AI: SIP, voice APIs, real‑time call handling

• Other tools & practices: CI/CD, automated testing, resilient architecture

Why Join Phonely?

We value a high‑energy team culture and offer a flexible, collaborative environment in San Francisco. By joining Phonely, you can contribute across all aspects of the business, work with a talented engineering group, and be part of a mission to deliver world‑class voice AI solutions to businesses worldwide.