I don't know why but a lot of spammers have my phone number and I'm getting called every day. I can't block their phone numbers because they use a new one every day. However, I use my phone with Slack and PagerDuty for work and I want to be able to hear notification sounds from those. How can I disable all sound for incoming calls (ideally, allowing certain known contacts to get through) while allowing certain apps as well?
One way would be to get a silent ringtone and set it as the default, then set another ringtone with actual sound for the contacts you want to hear calling. There are plenty of silent ringtones available to buy in the iTunes Tones store, but it would also be a simple one to create yourself.