Clay, I have a iPhone 11 Pro & the converting is done automatically. Same with my iPad. When I do like you said & click on, add a photo to an album or start a new nested album, a pop up appears to do the photo choosing uploading process. Perhaps you have pop ups blocked in your iPhone, as this has happened to me in the past, causing what you described. Presently with the new Apple OS18 I don’t see a way to control pop ups, though I just uploaded a couple photos with the iPhone using the latest OS18 & it went smoothly.
When using the iPhone or iPad & wanting to add a photo from my albums to a post, then it does have to be manually changed to a jpeg as Bob said. For me to do this, I switch from Safari to Chrome & even then a somewhat complicated process.
What has dramatically changed for me is adding video to an album. In the past it was easy to do with the process being identical to adding a photo & would go smoothly as long as the video was under a minute in length. During my Alaska cruise with my granddaughter this summer, I tried to upload video, as I have done in the past & it wouldn’t upload, no matter how short the video. I thought it was the lower upload speed, I had on the trip, but since getting back home it still won’t upload even with fiber optic speed. Other than a couple photos, I have for the most part given up photo & video uploading, until the changes, that Danag has said are coming, arrive, as I would like to arrange the photos & video in order of trip sequence, as I upload them.
Jay