Haven't we had this thread before?
Phone mostly portrait, because that's what the aspect ratio dictates for sensible handheld use, and most apps are designed to work that way. Usual exception for taking photos and recording/viewing video, which should almost never be portrait.
My tablet is 4:3, so works pretty well in either orientation. Landscape when the keyboard's attached, or when doing serious typing using the onscreen keyboard. Portrait for reading ebooks. Otherwise, whatever's most convenient at the time (often dictated by the presence of the charging cable on the short edge).
But generally, when not out and about or in bed, I prefer to use a real computer.