The 5e SRD mentions all eight schools as possible for the wizard's Arcane Tradition feature.
But later on it only describes evocation.
Does this mean the other seven (as described in the PHB) are not open per the SRD licence?
Yes, the details of the other traditions are not licensed under the OGL. The presence or absence of something in the SRD is the literal definition of what parts of D&D 5e have been licensed under the OGL (SRD 5.0 v1.1, p. 1, ¶ 2):
This material is being released using the Open Gaming License Version 1.0a
If it's not in the SRD, it's not open.