The construction of a Golay complementary sequence (GCS) set with small cardinality and flexible length has long been an open problem. Compared with the $2$-phase GCS pairs, more possible lengths were founded in literatures by extending the phase and the cardinality of the GCS set. For both mathematical theory and engineering applications, it is desirable to keep the cardinality of the constructed GCS set as small as possible. In this work, we construct a $4$-phase GCS set with cardinality $2^{3+\lceil \log_2 r \rceil}$ and arbitrary sequence length $n$, where the $10^{13}$-base expansion of $n$ has $r$ nonzero digits. Specifically, the 4-phase GCS octets (sets of eight sequences) cover all the lengths no greater than $10^{13}$.