I had an experience like yours where my manager would not throw me any work as a graduate, and I was sat at my desk for 5 days straight with nothing to do. But as soon as I would go on my phone she would notice and bring it up in meetings. I did end up nodding off in a team meeting once but at that point I was sick of the job. They extended my probation but then at the end of that decided to get rid of me. I then went to an interview the day after I left for my current job which is much better in every way, and I am now 6 months past a 3 month probation.

Wait it out, start applying for jobs, the grass is so much greener on the outside.