@SpaceInvader321 KS3 to KS4 is a change of key stage, but not a phase transfer. Similar to a child in reception in a primary school moving to Y1 changes from Early Years Foundation Stage to KS1, but it is not a phase transfer.
Infants to juniors is only a phase transfer where the child is in an infant school. It isn’t a phase transfer when a child is in a primary school where infants and juniors are in the same school.
DC can move outside of the phase transfer years via the AR process, an early review, or reassessment of needs, so if they need to move for Y9 or Y10, they can. Although the LA may force parents to appeal.