Make a short sound with their name in it, then assign it to that person in your contacts so it plays only when they call. You can record it yourself, use a text-to-speech voice, or use an app that sings it.
With Ringoz you say who the ringtone is for, type their name and a line such as "Mom is calling, pick it up", and pick a style, from Gospel Choir to Drill. The app sings it back as a finished 30-second ringtone and can set it for that one contact. On iPhone, you can also assign any ringtone in Contacts, under Edit and Ringtone.
Related questions
How do I set a different ringtone for each contact on iPhone?
Open the contact, tap Edit, then Ringtone, and choose the tone.
How can I make a personalized ringtone as a gift?
Make a ringtone with their name and an inside joke, then send them the audio file.
What are good personalized ringtone ideas?
Their name plus a line in their voice: a nickname, an inside joke, a catchphrase.