Mine's 17 months and sometimes she says phrases, "brush your teeth Wyatt", I remember that one lately because she used it wrong. Usually she uses her phrases right but this one she was calling a toothbrush a "brush your teeth Wyatt". Sometimes she says nice phrases like that, quite clearly. But she says them rarely. Mostly she squeaks and squawks and she does a lot of what you're describing, using only half words. She'll call a dog a og and a duck a uck and other times say them right. She'll go on a three day kick where she's using full sentences one right after the other all day long. Then it's a full month before she'll a full sentence again. She does the singing thing too, singing along to familiar songs with words she obviously doesn't know, but getting many syllables and notes in the right spot. I'm just saying that I see the talking more/talking less too. Obviously your doctor knows more than an Internet friend.
