Probably a scammer - this is a mobile phone. There is also no "Manna & Associates" registered with the Secretary of State for NJ.
There is a Michael Manna and Associates, in Ridgefield, NJ. However, he doesn't do debt collection - his practice concentrates on elder law, medicaid planning, estate planning, matrimonial & family law, divorce & child custody.
Remember - if your caller will not send you written proof that you owe this debt to them within five days of their call, do not pay!