Royal phone held by supporter (7)
I believe the answer is:
stately
'royal' is the definition.
(stately can mean royal or majestic)
'phone held by supporter' is the wordplay.
'phone' becomes 'tel' (short for telephone).
'held by' indicates putting letters inside.
'supporter' becomes 'stay' (a stay is a device providing support).
'tel' placed within 'stay' is 'STATELY'.
(Other definitions for stately that I've seen before include "Dignified and impressive" , "Imperial" , "Formal; type of home" , "` `In Xanadu did Kubla Khan / A ....... pleasure-dome decree' ' (Coleridge)" , "Impressive in manner" .)