Hi, OnlySal.
It appears that you're not hearing any ringtone when a particular person calls you. Instead, they're sent to voicemail and I'm happy to help.
Block phone numbers and contacts on your iPhone, iPad, or iPod touch -- See if that person's number has been blocked.
Use tones and ringtones with your iPhone, iPad, or iPod touch -- If their phone number isn't blocked, it may be the ringtone you've used. If you've selected a specific ringtone to sound when they call, make sure produces a sound when you tap it.
- On your iOS device, go to Settings > Sounds & Haptics.
- Tap the sound that you want to change. You can change your Ringtone, Text Tone, New Mail sound, Calendar Alerts, and more.
- Tap on the name of a ringtone or alert tone to hear it play and set it as the new sound.
You can also set a Ringtone or Text Tone for a specific contact. Find the person in the Contacts app, then tap Edit in the upper-right corner. Tap Ringtone or Text Tone and choose a new sound.
Let me know how that goes.
Take care!