The best thing to do is to download the manual.
But very briefly explained:
There are 12 analogue mic/line inputs on Phoenix and 12 analogue outputs on Phoenix.
Then there is an S-Link socket that allows you to connect A&H expanders or A&H mixers.
A slot in which you can insert various cards, e.g. a Dante card.
A network port for programming
A GPIO port for connecting external control voltages or for controlling external circuits.
A connection for the internal power supply
A connection for an external power supply unit