There are 2 types of audio interfaces to use while connecting your guitar to your phone: Analog Audio Interfaces and Digital (USB) Audio Interfaces. We recommend you to use USB interfaces because they offer higher quality with lower audio latency. Check the following link to see the list of our suggested interfaces:
TC Helicon Go Guitar is one of the analog audio interfaces that are compatible with mobile devices.
Also, there is iRig and iRig2, which can be found easily online and in stores.
My favourite analog audio interface is BandLab: https://deplike.com/blog/audio-interfaces/how-to-connect-your-guitar-to-your-android-phone-tablet-iphone-or-ipad-using-bandlab-analog-mini/
Although it is best to use USB audio interfaces with Android devices in order to utilize Deplike’s own USB driver for top quality audio, this little interface is perfect for use on iOS devices.
Check out this BandLab Analog Mini review video: