Most public libraries have them. A large part of the patron base of the public library in 2024 are people who are marginalized and a lot of them come to the library because they lack other internet access. There's also the elderly, the disabled, etc.

The main problem is that libraries don't run the staff levels to make in-depth phone reference feasible, and a lot of public libraries don't have advanced level/academic knowledge available in their hardcopy print collections + don't have people on hand with that level of specialty knowledge to provide high level and in depth answers efficiently (if given a choice, hiring a children's librarian makes far more sense for a public library than a physics expert, but she probably can't answer high level physics questions).

Academic libraries have the subject expertise, but those librarians' time is too planned and valuable to spend on phone reference. Chat reference is usually shared across institutions with librarians in different locations to allow for sharing the work and deduplication of work - one subject area specialist can do chat reference for multiple institutions.

There are plenty of people around who can still do this, but they're usually paid to do other things instead.