Of cours you can!! UPES Hostels are not some kinda rock prison where you cannot keep an amenity as basic as mobile phone! But yes, you and only you are responsible for any loss/theft of mobile phones. I have had an ugly tryst with my new smartphone back when I was a student there, although not a resident of the Campus Hostel.
So if you take my word, primarily look after your phone while exam times. Campus hostels are safe!