It’s not Phoenix, it’s Elixir, and it depends how You install it.
I use asdf-vm, and can list all versions, and install the one I want.
$ asdf list-all elixir
...
1.13.4
1.13.4-otp-22
1.13.4-otp-23
1.13.4-otp-24
main
main-otp-22
main-otp-23
main-otp-24
master
master-otp-21
master-otp-22
master-otp-23
master-otp-24
The version I would use…
1.13.4-otp-24
