Stay in bed a bit longer - left, that is, at home (3,2)
I believe the answer is:
lie in
'stay in bed a bit longer left that is at home' is the definition.
'lie in' can be an answer for 'stay in bed' (I've seen this before). I am unsure of the rest of the definition.
'left that is at home' is the wordplay.
'left' becomes 'l' (common abbreviation).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'l'+'ie'+'in'='LIE-IN'
Can you help me to learn more?
(Other definitions for lie in that I've seen before include "stay longer beneath the sheets" , "An extra spell in bed" , "Get up late" , "Rise late" , "Long stay in bed in the morning" .)