Ring mobile phone: exploit hospitality for all (4,5)
I believe the answer is:
open house
'hospitality for all' is the definition.
(hospitality for all visitors)
'ring mobile phone exploit' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'mobile' is an anagram indicator (mobile can mean moving).
'exploit' becomes 'use' (use can mean to exploit).
'phone' is an anagram of 'penho'.
'o'+'penho'+'use'='OPEN HOUSE'
(Other definitions for open house that I've seen before include "Hospitality to all comers at home" , "Event with hospitality to all comers" , "Keep this to welcome all comers and guests" , "showing hospitality to all?" , "Total hospitality" .)