Pewee was my first thought also. What led me phoebe-ward was the darkish head and the (apparently) all-black bill.
Seems pewee can have dark bills. See the bird in the allaboutbirds link for instance.
Don't think so; in my experience the under mandible's always pale and is invariably so depicted in field guides. That's why I used the word "apparently" in my previous post, to indicate that the bill wasn't necessarily really all-dark but that that's how it appeared in the photo.
Here is what I found in two guides near me at the moment:
The Eastern Wood-Pewee "juveniles can have all dark bills" Natl. Geo bird guide 6th edition p. 329 (on the plate). "Juvenile and immature may have all-dark bill" p. 328 (facing-page text).
Western Wood-Pewee "base of lower mandible usually shows some yellow-orange" which means that it sometimes appears all dark p. 328. Note that the illustrations for both species show at least some orange on the bill.
Pyle's Identification Guide to North American Birds, for Western Wood-Pewee states and illustrates "underside of lower mandible usually primarily dark (Fig. 142A-C)" p. 215.
The eastern Crossley Guide portrays a couple of Western Wood-Pewees with really dark bills, p. 336.
It's subtle, but it doesn't feel normal for an eastern phoebe. Head shape, wing bars, even the greyness of the belly and shape of dark hood extending down the cheeks. I'm not familiar with olive-sided but judging by photos, olive-sided would be darker, with fainter wing bars.
However, I think we can rule out wood-pewee based on primary projection. Either it's an odd-looking eastern phoebe or we are overlooking some other options.
Silverwolf, look again at the length ratio of primaries to secondaries. In my books the wood-peewee primaries extend past the secondaries by about 75% , while the phoebes, like the photo here, are closer to 50%. Not sure what the range of variability is, and maybe i'm just measuring poorly.
I also didn't really take the time to look at the image and was too occupied with the idea it was a pewee. The % you suggest is correct...