Android users have had the Droid-Star app for this purpose for quite a while but recently a beta version for iOS has surfaced which can be tried by ham radio operators on the iPhone. The video below takes you through the steps to install it via the Test Flight app.
Just to note for DMR you need to have also created (under SelfCare on the Brandmeister website in your Profile) a password by HotSpot security after enabling that setting. This password must be set inside this app's settings too. The Tx button is a toggle button so you need to kerchunk it (tap twice) to register in the Talk Group.
Interesting that this iOS version is a branch off the DUDE-Star Github project and that main branch can also compile to work on Linux, Raspberry Pi and MacOS (with Windows executable only downloads under Releases in the project).
See How to install Droid star on iPhone
https://github.com/nostar/dudestar/discussions/129if you are are in a country that requires a password for your hotspot security or air security you may nee...