Part of foot trapped in toilet locks mobility aid (10)
I believe the answer is:
wheelchair
'mobility aid' is the definition.
(I've seen this before)
'part of foot trapped in toilet locks' is the wordplay.
'part of foot' becomes 'heel' (heel is a part of the foot).
'trapped in' indicates putting letters inside.
'toilet' becomes 'wc' (W.C. is an example).
'locks' becomes 'hair' (I've seen this in another clue).
'heel' put inside 'wc' is 'wheelc'.
'wheelc'+'hair'='WHEELCHAIR'
(Other definitions for wheelchair that I've seen before include "Mobility aid" , "Invalid's transport" , "Invalid transport" .)