I Witnessed A Case Of A Cellphone Left Behind

This story is a throwback . It happened many months ago, but I cannot forget this incident.
While I was eating at a fast food chain alone after my shopping , I noticed a phone with a plugged powerbank , at the front table where a sole woman also, have just eaten and left.
I looked around to call her but she was gone and then saw a girl and a boy in their 20’s bringing a tray of what they ordered looked around, saw the now vacant table and went straight to the said table.
I immediately went to the crew at the service counter and reported about the cellphone left behind by a woman who have just left. But they were busy and just take a look at the table now being occupied by a girl and a boy.
Then after that , I approached the two new occupants of the table and and told him that a woman who has just eaten there , forgot t the cellphone with aplugged powerbank . The boy said that the phone is his and lifted it up and scrolled at it.
I was speechless and felt like telling him how can it be yours when before you two came it was there already.
But I kept silent, because they might harm me since there’s the two of them and could be part of a syndicate who is into stealing others’ cellphones as I have seen on TV.
The crew told me also when I went to the service counter, that they might be the woman’s companion, but I know they’re not at all!
I felt guilty not picking it up at once and surrendering it to the manager of the fast food chain, when the woman left and forgot her phone.
How can people be so daunting, to be dishonest like that!
But then, I did my best, reported it, however, what happened next was so fast
I cannot argue with the two persons who claimed that the phone were theirs, when I know that it’s owned by the woman who just left before they occupied the table.
I was also scared of what the two of them can do to harm me. Would you be too, if you were in my stead?

Note: The picture is from google .