I've definitely had this problem. There were times I lost my phone and had to get back home. No one would let me use their phone. It was not until I begged a gas station attendant to let me call someone I knew who could pick me up, that I was able to get home.

Only anecdata, but I’ve experienced it directly, and I’ve also helped other people out when I saw them experiencing the same. I’m a little surprised by this response to be honest?

My personal experience is that I have never had someone decline to let me use their phone. I believe people are default kind and interested in helping others, and it's hard to imagine that in a random sample of say, 5 people, none would let you use their phone for a few minutes.