There used to be a particular restaurant I ordered from. It was a real restaurant, not a ghost kitchen. It was listed on Uber Eats and similar, but you could also order from them, which was significantly cheaper. We used to have an image of the menu and the phone number but eventually lost it. Because the restaurant was only listed on Facebook, none of us have a Facebook account, and Facebook aggressively tries to keep you out without an account, it was a royal pain to get the number back. But even after getting the phone number, it was WhatsApp only. Which I don’t use. Some of my friends do, so that was taken care of like that.

There was another place which was on the brink of closing and kept shifting its opening hours and days. I went there on occasion but because there was no official web presence I couldn’t trust the hours online (photographs of the schedule). So I called. Sometimes they picked up, sometimes they didn’t. When they didn’t, sometimes they were closed but other times were just busy and couldn’t come to the phone.

So no, you can’t always find a phone number, and you can’t always call and ask. Having a roughly up-to-date web presence is very useful. It doesn’t need to be a bespoke website, you can use a platform, just don’t exclusively use closed garbage like Facebook and Instagram which walls you off from customers.

From my experience, you can't count on businesses to update their website to correctly reflect their working hours at all times either (especially if it's a one-off change, for example being closed for a day)