Over the phone, picture best wild plant (3,4)

'wild plant' is the definition.
(type of plant)

'over the phone picture best' is the wordplay.
'over the phone' indicates a 'sounds like' (homophone) clue (how it might sound over the phone).
'picture' becomes 'see' (synonyms).
'best' becomes 'beet' (I can't justify this - if you can you should give a lot more credence to this answer).
'see' sounds like 'sea'.
'sea'+'beet'='SEA-BEET'