You can do that, yes. I believe that lateral moves between DRL airframes is not allowed (or was not) so you can't do Phenom 2 years, Praetor 3 years and then Challenger 3 years then back to Praetor etc. so just be cognizant of that when the time comes to have upgrade bids in to DRL. Also if you're interested in ILC upgrading into the Phenom puts you in better standing than remaining as an FO regardless of seat. Commanders are looking for pilots who have already upgraded when they're selecting their teams.