There are a growing number of mobile apps you can use with PieFed:
See also this wiki page.
Or, use the web app on your phone. It’s fine, really.
PieFed is a ‘Progressive Web App’ meaning it is a website that can be installed into your phone as if it was a real app. The general idea is you open PieFed in your web browser and then look for the function in the web browser that installs it. The details vary a bit depending on the type of phone you have and the web browser you use.
First scroll all the way down to the bottom and look in the footer for a button saying ‘Install PieFed app’. If that button is not there then possibly your browser doesn’t support PWAs.
Also try this: tap the 3 dots in the top right (in Firefox the three dots could be in the bottom right), then when the menu appears, tap ‘Add to home screen’ and then on ‘Install’.
That’s all! From now on instead of going to the website in your browser you can find the PieFed icon in your apps and tap that instead.