"Lightest phone" refers to a mobile device that weighs the least among similar phones. It means the phone is very light and easy to carry. Full definition
The first phone could only make calls and tell time, about as minimal as a phone could be in 2015, when the original Light Phone came out. (relevantmagazine.com)
This isn't one of those paper light phones that puts you off, nor is it a heavy bulky phone. (mobilegeeks.com)
Yes there are lighter phones available, and like I always mention buy the handset as per your needs. (gogi.in)