Phillips' Crystal Palace face the Baggies today.
"I was very, very surprised they let him go," Phillips told the Birmingham Mail. "We know what the problems were with the previous manager (Paolo Di Canio) but as soon as I saw him pitch up at West Brom I thought that was a great move.
"I still have a lot of friends at Sunderland and they are surprised he was allowed to go but I guess there were a few players who fell out with the previous boss and had no option but to leave.
"On his day Sessegnon can tear any team apart. He is a very impressive player and one we'll have to watch this weekend."
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