On iOS running devices, you can easily set a specific ringtone for a specific contact. To assign and change ringtone for a contact on iPhone, do as follows:
1. Open the Contacts application on your iPhone
2. Tap the Contact you'd like to assign a specific ringtone to
3. Tap the Edit option on the top right
4. Scroll down to Ringtone and set a ringtone for this contact on your iPhone.
Tip: You may also assign a specific vibration pattern or text tone to your selected contact.