Doctor forgets net worth of such a stalwart (5,2,8)
I believe the answer is:
tower of strength
'such a stalwart' is the definition.
(thesaurus)
'doctor forgets net worth' is the wordplay.
'doctor' indicates anagramming the letters.
'forgets'+'net'+'worth'='forgetsnetworth'
'forgetsnetworth' with letters rearranged gives 'TOWER OF STRENGTH'.
'of' acts as a link.
(Other definitions for tower of strength that I've seen before include "Person giving support" , "one pulling a lorry by rope?" , "tugboat?" , "One's extremely dependable when needed" , "Great support" .)