You group with her for awhile and she actually appears to be a nicer person. Except of course for one thing the main character wont like: Pheare is trying to win Sola back.
So now Sola is trapped between staying with the main character, or going back to Pheare, a woman he believes had died because of his part in the whole dragon egg switching--and who has forgiven him.
Ohhh.... the plot thickens. Tho I think the PC should have the right to say something along the lines of, "Hello! I got tortured AND I got my soul stolen from me and I saved you -TWICE!-" (First being sparing Sola's life in the Underdark, and twice from getting him back from Bodhi.)
This is how I would role play as Phaere :
After dying the way I did in Ust Natha I'd want revenge, and I'm probably getting tortured to boot while I'm in FR's version of Hell.
Plenty of time to think of a master plan on how to get back at Sola and the main character.
I see the Pocket Plane forming and enter much in the same way as Sarevok did. Then I notice that Sola and the main character are together and appear to be lovers. What better way to break even then by destroying the bond between Sola and the main character? Motivated by jealousy of not being able to remain in love with Sola while I had been alive--or just out of pure spite-- I wanted to destroy them.
So I ask for forgiveness and pretend to learn the error of my ways, hoping to weaken the bond between Sola and the main character, and then ruin them once I have them seporated.
::turn off roleplay::
The same idea of an argument the main character could have with Sola could be the beginning of the rift between the two. Depending on how you react you can push Sola towards Phaere--which would lead to Phaere trying to kill him once he's 'vulnerable' and thus you have the option to save him or letting him die. Or you can choose to try to keep Sola and prove to him that Pheare is trying to destroy the love between you and him.