Three is the number that flatters people
An odd number of slots gives one picture more room than the others, and a face in that slot reads as the subject rather than one of a set. That is why three keeps turning up in printed layouts and why it survives being looked at on a phone: even at story height the lead slot is over six hundred pixels tall, which is enough for an expression to carry.
Four photos split a square into quarters and every quarter is equal, which is fine for objects and flat for people. If you have four good pictures and one of them is better, three of them arranged here will usually beat all four in a grid.
What the five do differently
Three columns and three bands are the even pair, and the interesting thing about them is what they become in a different shape: the columns turn into rows down a story, because three vertical slices of a 1080 by 1920 picture are 360 pixels wide and nothing survives that.
One over two and one beside two are the lead layouts. Put the widest photo in the big slot — a landscape in the lead of the first, a portrait in the lead of the second — and the two small ones stop competing with it.
Stepped three is the awkward-set layout. Two of unequal width above a full-width band means a photo that is nearly square, a photo that is very wide, and a photo you are not sure about can all sit together without any of them being cropped to death.
Where three goes wrong
Three photographs of the same scene, taken seconds apart, make a collage that looks like an accident rather than a choice. Three that differ in distance — one wide, one at chest height, one close — read as a small story, and the layouts here are drawn on the assumption that you have the second kind. If all three are similar, the even layouts hide it better than the lead ones do.