  We study an axion-like particle (ALP) that experiences the first-order phase
transition with respect to its mass or potential minimum. This can be realized
if the ALP obtains a potential from non-perturbative effects of SU($N$) gauge
theory that is confined via the first-order phase transition, or if the ALP is
trapped in a false vacuum at high temperatures until it starts to oscillate
about the true minimum. The resulting ALP abundance is significantly enhanced
compared to the standard misalignment mechanism, explaining dark matter in a
broader parameter space that is accessible to experiments e.g. IAXO, ALPS-II,
and DM-radio. Furthermore, the viable parameter space includes a region of the
mass $m_a \simeq 10^{-7} - 10^{-8}$ eV and the ALP-photon coupling $g_{a \gamma
\gamma} \simeq 10^{-11} {\rm GeV}^{-1}$ that can explain the recent observation
of very high energy photons from GRB221009A via axion-photon oscillations. The
parameter region suggests that the FOPT can generate the gravitational wave
that explains the NANOGrav hint. If the ALP in this region explains dark
matter, then the ALP has likely experienced a first-order phase transition.
