By the sounds of it I'd say she definitely has glue ear especially if it comes and goes...the movement of the phlegm etc.
My eldest DD had glue ear from a very early age and it was picked up during her routine hearing tests pre-school. Each time I was fobbed off by the ENT people saying she'd grow out of it etc etc. She failed hearing test after test and yes, it concerned me but because I didn't know any different I went along with the theory she'd grow out of it.
During her first year of school her confidence took a nose dive, she wasn't paying attention at school and had ear infections galore. She had a routine hearing test at school which, again, she failed. We left it till the weather became warmer in the hope the coughs and colds would clear up and she was tested again - again failed.
We were then referred back to ENT who again told us she'd grow out of it.
Her behaviour at school was getting worse - she wasn't naughty but she wasn't paying attention and was having to sit at the front of the classroom. She was also very nasaly and always talked as if she talked thru her nose. She always had colds and regular ear trouble.
I decided, by the time she was going into Year 1, that I wasn't going to wait for her to grow out of it because she's a bright child and I didn't want her to slip at school so we went private. The consultant we had was horrified the NHS suggested she would grow out of glue ear - she was stone deaf in one ear and only partially able to hear in the other.
She was admitted to a private hospital, had grommits fitted, addenoids removed (flaps of skin at the back of the nose which prevents phlegm from moving around) within the week.
Following that operation she complained immediately we were talking too loud!
Prior to this she wouldn't hear us, we'd have to shout, if we covered our mouths when talking to her she wouldn't know what we were saying because she'd taught herself to lip-read, she wasn't as snotty, no ear infections and it was the best £2k we'd ever spent...well, the credit card did!
I would definitely get an appt for a hearing test, without delay, especially as she is coming up to the age of starting school. Good luck!