Find and Kill PID from Previous Phoenix Session [Phoenix/Elixir]

Question

To Stop Processes Resulting from mix phx.server Command in Previous Session

• I ran mix phx.server
• I did not type ctrl-c x2 to terminate the resulting processes
• I quit the my text editor
• I try to rerun mix phx.server and get this error:

What I've Tried

To View the Process

• lsof -i :4000/:5432/:8080
• netstat commands
• Activity Monitor

To Kill the Process

• kill -9 <PID> to no avail because I still can't find the right PID for that previously run phoenix session.

Also, the error for "failed to start child" is not the cause of me being unable to run mix phx.server it's because I didn't close the previously existing process