  We consider the Aharonov-Bohm (AB) effect on a confined electron ground state
in a quantum ring defined electrostatically within the phosphorene monolayer.
The strong anisotropy of effective masses in phosphorene quenches ground-state
oscillations for a circular ring because of interrupted persistent current
circulation around the ring. An elliptic deformation of the confinement
potential can compensate for the anisotropy of the effective masses and produce
ground-state parity transformations with the AB periodicity. Moreover, a
specific ratio of the semiaxes is determined for which the spectrum becomes
identical to that of a circular quantum ring and an isotropic effective mass.
We identify a generalized angular momentum operator which commutes with the
continuum Hamiltonian for the chosen ratio of the semi-axes that closes the
avoided crossings of energy levels for states of the same parity and spin.
Ground-state oscillations for the two-electron ground state are also discussed.
