The Libyco-Berber script is a fairly strict abjad, in which only consonants are written. The principal exception is H, which word-finally seems to mark vowels. The transcriptions used in the principal reference for Libyco-Berber inscriptions, RIL, is as follows:
(source: Chabot, J.-B. 1940. Recueil des Inscriptions Libyques. Paris: Imprimerie Nationale.)
Of these, U and I are better transcribed W and Y, to reflect their consonantal value, while Ç corresponds to Punic ṣ. The phonetic differences between the various Z's and T's are not certain. See Kossmann (2020) for the range of possible phonological analyses of the sibilant system, and van Putten (2017) for the possibility that T1, rather than having been pronounced as /t/, may just be an allograph of H.
Some letters' values are not certain, particularly in the Western inscriptions, due to lack of bilingual texts containing them. These include (according to RIL):
Some of these, however, may just be variants of better-known letters.