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.