  The CKM angle $ \phi_{3} $ is the only angle of the unitarity triangle that
is accessible with tree-level decays in a theoretically clean way. The Belle II
experiment is a substantial upgrade of the Belle detector and will operate at
the SuperKEKB energy-asymmetric $ e^{+}e^{-} $ collider. The accelerator has
already successfully completed the first phase of commissioning, with the first
$ e^{+}e^{-} $ collisions recorded in 2018. The design luminosity of SuperKEKB
is 8$ \times 10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to
record 50 ab$ ^{-1} $ of data, a factor of 50 more than the Belle experiment.
The key method to measure $ \phi_{3} $ is through the interference between $
B^{+} \to D^{0}K^{+} $ and $ B^{+} \to \overline{D}^{0}K^{+} $ decays, which
occurs if the final state of the charm-meson decay is accessible to both the $
D^{0} $ and $ \overline{D}^{0} $ mesons. To achieve the best sensitivity, a
large variety of $ D $ and $ B $ decay modes are required, which is possible at
the Belle II experiment as almost any final state can be reconstructed,
including those with photons. With the ultimate Belle II data sample of 50 ab$
^{-1} $, a determination of $ \phi_{3} $ with a precision of 1$^{\rm o} $ or
better is foreseen.
