If you use Ai for therapie atleast selfhost and keep in mind that its goal is not to help you but to have a conversation that statisvies you. You are basicly talking to a yes-man.
Ollama with OpenWebUi is relativly easy to install, you can even use something like edge-tts to give it a Voice.
The smallest Modells that I run on my PC take about 6-8 GB of VRAM and would be very slow if I ran them purely with my CPU. So it is unlikely that you Phone has enough RAM and enough Cores to run a decent LLM smootly.
If you still want to use selfhosted AI with you phone, selfhost the modell on your PC:
You now can use selfhosted AI with your phone and an internet connection.