Design plug-in memory device on a phone, originally (4,3)
I believe the answer is:
road map
'design' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'plug-in memory device on a phone originally' is the wordplay.
'plug' becomes 'ad' (as in plugging a product).
'in memory device' becomes 'roma' (I can't explain this - if you can you should believe this answer much more).
'on' indicates putting letters inside (as in clothing 'on' a person).
'originally' says to take the initial letters.
The initial letter of 'phone' is 'p'.
'ad' going inside 'roma' is 'roadma'.
'roadma'+'p'='ROAD-MAP'
Can you help me to learn more?
(Other definitions for road map that I've seen before include "Plan for peace process" , "Document detailing route to an end" , "Guide" , "superseded by satnav?" , "strategy for peace?" .)