Senior Backend Engineer (Series A Backed)

Phonely; San Francisco (CA); On-site; USD 120,000 - 160,000; Full time

Job summary

Phonely is looking for a Senior Backend Engineer in San Francisco. The role involves designing, building, and maintaining Python-based systems for voice AI applications. Responsibilities include integration of various LLM providers, writing clean, high-performance code, and implementing security mechanisms. The ideal candidate has over 5 years of experience with Python, AWS, Kubernetes, and a solid understanding of CI/CD pipelines. This is an in-office position, requiring collaboration in a dynamic development environment.

Qualifications

• 5+ years of experience writing Python, including async web apps using FastAPI and testing frameworks.
• Strong understanding of LLMs, APIs, cloud, and CI/CD pipelines.
• Excellent communication skills with great teamwork and collaboration.

Responsibilities

• Build and maintain Python–based systems for voice AI.
• Integrate multiple LLM providers and design prompt strategies.
• Write clean, maintainable, high‑performance Python code.

Skills

Python

FastAPI

CI/CD

AWS

Kubernetes

Security best practices

Teamwork

Tools

Datadog

Firebase

Supabase

Redis

Job description

Senior Backend Engineer (Python)

This role is in office 5 days a week in San Francisco.

About the role

We are building voice AI for businesses and want an experienced engineer to help design, build, and maintain the systems that drive real‑time conversations. The role is highly dynamic, requiring deep technical expertise and a hands‑on approach.

Day to Day 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.

Qualifications

• 5+ years of experience writing Python, including async web apps using FastAPI and testing frameworks.
• Strong understanding of LLMs, APIs, cloud, and CI/CD pipelines.
• Comfortable interpreting technical specifications and designing sound architecture.
• Knowledge of security best practices in backend development.
• Excellent communication skills with great teamwork and collaboration.
• Experience with AWS and Kubernetes, and managing scalable infrastructure.

Our Software Stack

• Backend: Python, microservices, async programming.
• Cloud & Infrastructure: AWS, GCP, Kubernetes, Redis.
• Databases: Firebase, Supabase.
• Observability & Monitoring: Datadog, logging, metrics, tracing.
• Telephony & Voice AI: SIP, voice APIs, real‑time call handling.
• Front‑end: Next.js.
• Other tools & practices: CI/CD, automated testing, resilient architecture.