Pilots may depart VFR and get IFR clearance while enroute.

Treat an aircraft planning VFR for the initial part of flight and IFR for the latter part as a VFR departure. Issue a clearance to this aircraft when it requests IFR clearance approaching the fix where it proposes to start IFR operations. The phraseology CLEARED TO (destination) AIRPORT AS FILED may be used with abbreviated departure clearance procedures.

When a VFR aircraft, operating below the minimum altitude for IFR operations, requests an IFR clearance and you are aware that the pilot is unable to climb in VFR conditions to the minimum IFR altitude:

Before issuing a clearance, ask if the pilot is able to maintain terrain and obstruction clearance during a climb to the minimum IFR altitude.

NOTE-
Pilots of pop-up aircraft are responsible for terrain and obstacle clearance until reaching minimum instrument altitude (MIA) or minimum en route altitude (MEA). Pilot compliance with an ATC instruction transfers that responsibility to the controller; therefore, do not assign (or imply) specific course guidance that will (or could) be in effect below the MIA or MEA.

PHRASEOLOGY-
(Aircraft call sign), ARE YOU ABLE TO MAINTAIN YOUR OWN TERRAIN AND OBSTRUCTION CLEARANCE UNTIL REACHING (appropriate MVA/MIA/MEA/OROCA)

Example-
LAS_APP: "N123AB, are you able to maintain your own terrain and obstruction clearance until reaching 6,500?"

If the pilot is able to maintain terrain and obstruction separation, issue the appropriate clearance.

If unable to maintain terrain and obstruction separation, instruct the pilot to maintain VFR and to state intentions.

“{Reference: FAAO 7110.65 4-2-8}”