Weep about phone game that's useless (6)

'useless' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

'weep about phone game' is the wordplay.
'weep' becomes 'cry' (synonyms).
'about' is an insertion indicator.
'phone game' becomes 'app' (I am not sure about this - if you are sure you should believe this answer much more).
'cry' placed around 'app' is 'CRAPPY'.

'that's' acts as a link.

Can you help me to learn more?