They build mud nests, not unlike many of the swallows, and attach the nests to a vertical surface, preferably one with a ledge on which to anchor the nest. Our window casing made the perfect site from the birds' point of view. It was an opinion that my mother didn't share but she always tolerated their mess until their families were raised and fledged, and, consequently, I was able to spend many happy hours observing them up close and personal. They were one of the first birds that I learned to identify by its proper name. Not hard since the bird tells you its name every time it opens its beak to sing - "feebee, feebee."
Eastern Phoebe keeping an eye open for flying insects it can scoop up.
For the last few years, I've had a phoebe resident in my yard for the entire winter and I assume that the one of the ones that I heard this morning is that same bird. There were actually two of the birds present today.
The little flycatchers abandon my yard in late spring, heading farther north to breed and raise their families, but I always look forward to their return in the fall and to the first time I hear that "feebee, feebee" that I remember so well from my childhood. I will duly note in my eBird report that this year the birds announced their return on November 7.