Wa'alaikumassalam! Sakit tekak masa pregnant memang mencabar, I totally get it, a few of us mums went through the same thing, and it's extra worrying thinking about what's safe to take. Best thing is to check with your gynae or clinic doctor first to confirm it's not something yang perlu antibiotics, especially since you're having trouble swallowing and the phlegm buildup, okay? In the meantime, try warm salt water gargles, honey in warm water, and stay super hydrated, one of my mum friends swore it helped her a lot during pregnancy!