Having lived in Phobsborough, and now living in "Glasnevin North". these are both relatively good areas.
Phobsborough is near town, loads of buses - loads of life, pubs, the community is mixed, you have students, home owners etc which gives the area a different vibe to Glasnevin. Glasnevin is a lovely village, and would be quieter than phibsborough.
There is a pub in Glasnevin called the Tolka house, across the road are nice apartments that would be reasonable enough to rent. You are also near to the Grave Diggers Pub [broken link removed] there..
Your friend should get an 83 from town out some evening, got out at the Tolka Valley pub and walk back to Phibsborough - this would give him a feel for both areas..
P..