"Dialing" a phone is niche functionality that most people don't use anymore - generally, people don't know phone numbers anymore, they don't really see them, and they definitely don't use them, they just tap on a name or face in their contact list.
A phone number is an identifier that you use once when obtaining a contact (or it gets shared by someone, so you don't enter it even that one time). If a phone actually required you to dial a number, for many people it wouldn't be usable as a phone to call their friends.
This means that integration with wherever users have stored their contracts (and right not it's generally one of the cloud services) is a key component of the dialer app, possibly the main one - a contact app without phone features can be used to communicate with everyone (using the multitude of VOIP services available, skype calls or whatever) but a dialer without contacts isn't sufficient for communication.
Not so sure about this... just yesterday I got stuck behind a freight forwarding truck that was labelled with only the company name, a list of destination ports, and a phone number.
Lawyers, doctors, and bail-bondsmen still advertise via their phone number. Entire generations still go to phone numbers as their primary means of reaching someone remotely.
Yes, this is the (rare) use case for the first call you make to a stranger. If you have a pre-existing relationship with a particular lawyer or doctor, you tap on their name or face in the contacts app.
Like, thinking about this I understood that don't know the phone number of my wife. I (probably?) have it written down somewhere outside my phone, I had known it by heart many years ago, but life was different back then, and as far as I recall it may be that I have not used it in any meaningful way for more than full ten years.
I recall that I have given her phone number to others on some occasions, but it involved sending a contact - possibly the number was displayed at the screen during that process, but neither I nor the receiver really read it, and it that way even before smartphones were a thing and sharing a contact happened over SMS.
A phone number is an identifier that you use once when obtaining a contact (or it gets shared by someone, so you don't enter it even that one time). If a phone actually required you to dial a number, for many people it wouldn't be usable as a phone to call their friends.
This means that integration with wherever users have stored their contracts (and right not it's generally one of the cloud services) is a key component of the dialer app, possibly the main one - a contact app without phone features can be used to communicate with everyone (using the multitude of VOIP services available, skype calls or whatever) but a dialer without contacts isn't sufficient for communication.