Pip case manager

Good evening,

I am my sons appointee for pip I made a claim back at the beginning of march as he is currently on dla we had the text from the pip assessor's to say they had his claim and if he needed a assessment they'd be in touch that was 6 weeks ago I called today to see if there was an update and was told it is with a case manager and if I haven't heard anything by the 11th of June to call back but he hasn't yet had an assessment so what does this mean will they call to arrange an assessment I don't quite understand the case manager and what yhey do.

Thanks in advance