I had loads of phlegm while smoking, tapered off during the transition to vaping until I was clear. However, it's started coming back, not much, quite light and only slightly slimey, but still phlegm.
A couple of times recently I've woken up during the night and felt that nasty "I'm clear and breathing freely and deeply, but I'm not getting enough oxygen in and am short of breath" feeling. I developed emphysema while smoking which is permanent damage to the alveoli so my lungs are a bit iffy and VERY sensitive e.g. a bunch of people inhaled some dust, everyone else was fine but I had to go see my doctor 'cause I thought the end was nigh.
Vaping liquid is oily and I suspect it can hinder oxygen transfer when it recondenses in the lungs. I've carried on with my emphysema medication and I reckon that's what's bringing out the, what I shall christen, 'e-phlegm'.
The negetive effects of vaping on the lungs are no doubt a fraction of those caused by smoking and younger and healthier lungs will not even notice them, but in my experience, they still exist. I'm very, very thankful to have given up smoking through vaping, but I realise I'm going to have to start cutting back on vaping in the near future as well.