Hey there, and welcome to Apple Support Communities, Dorothy Rich!
From our understanding, your ringtone keeps changing on your iPhone. We’d be happy to take a look, as we know how important it is that you’re able to personalize your iPhone with ease.
First, if you’re using a ringtone that was purchased or custom made, let’s try selecting one that came pre-downloaded on the device. For example, if you change your ringtone to Apex, does it revert to Reflection or stay the same?
If it stays the same, and you’re using a purchased or custom made ringtone, does the same thing occur if you change it to a different one? This can help us to isolate whether it’s a specific ringtone that this is occurring with.
Also, which iOS version are you currently on? You can find that in Settings > General > About.
Cheers!