A verb has conjugation (спряжение), a noun has declension (склонение). We conjugate verbs, and we decline nouns.
So, it should read "a verb with incomplete conjugation".
Yes, it is incomplete:
надлежу impossible
надлежишь impossibble
надлежит OK
надлежим impossible
надлежите impossible
надлежат impossible
present tense: Мне (тебе, ему, ей, нам, вам, им) надлежит.
past tense: Мне (тебе, ему, ей, нам, вам, им) надлежало.
It is impersonal only, it cannot have a grammar subject in Nominative.
Usage: Dative (to whom) + надлежит (надлежало) + infinitive (to do something).