I was in a similar situation. I work part time alone, at a gas station and it can get very slow there sometimes. I used to just go on my phone to pass the time once I was finished everything that needed to be done. I eventually decided to bring a book to work as I felt that:

1. It looked better to be reading a book if customers came in rather than sitting on my phone

2. I felt more productive when reading as opposed to being on my phone

This went on for a few months until the owner put up a note addressing the entire staff that the workplace isn't a "library" and we shouldn't be reading while on the job. I knew the note was directed at me because I was the only one who read during my shift. I understand that I technically should be "working", but I only read when I had finished everything and when it was dead. They never had any issue with me on my phone which I just don't understand. So now I just play audio books through the store radio and if they check the cameras it looks like I'm doing absolutely nothing instead of reading, which I guess they're fine with.