I found this video on how to create my own custom ringtones for my iPhone (or android). It is a little old but still works well. I’m using iTunes version 12.5.5.5.

Here is a summary of the steps:

1. Open iTunes and select a song.
2. Right click on the highlighted song and select “Get Info”.
3. Click on the “Options” tab.
4. Check both boxes next to “Start” and “Stop” – This is the start and stop times you want to use as a ringtone. (I believe the tone length has to be less than or equal to 45 seconds. Anything longer will not be recognized by iPhone as a ringtone.)
5. Click “OK”
6. From the file menu at the top left of iTunes select “Convert” > “Create AAC Version”. This will create a copy of the file and place it directly underneath the original file.
7. Highlight the original file and turn off the check boxes next to “Start” and “Stop” to restore the file to its original condition.
8. Now, drag and drop the new, AAC file, to your desktop.
9. Rename the file extension on your desktop to .mp3r or .mp4r.
10. Delete the ACC version inside of iTunes
11. Drag and drop the .mp3r or .mp4r file from your desktop to your “Tones” folder in iTunes.
12. Connect your iPhone to your computer and synchronize the tones folder.  (Note: Sometimes my computer recognizes my iPhone without plugging it in.)

Let me know if you run into any trouble.