Ordering option: porter brought round a trolley (1,2,5)
I believe the answer is:
a la carte
'ordering option' is the definition.
(I've seen this in another clue)
'porter brought round a trolley' is the wordplay.
'porter' becomes 'ale' (type of beer).
'brought round' indicates putting letters inside.
'trolley' becomes 'cart' (I've seen this in another clue).
'a'+'cart'='acart'
'ale' enclosing 'acart' is 'A LA CARTE'.
(Other definitions for a la carte that I've seen before include "With each dish chosen separately" , "The pick what you please menu" , "It suggests lots of possibilities" , "Menu of individual dishes with separate prices" , "Menu with items indiviually listed and priced" .)