  We investigate a new class of galactic halo axion detection techniques based
on precision frequency and phase metrology. Employing equations of axion
electrodynamics, it is demonstrated how a dual mode cavity exhibits linear
mode-mode coupling mediated by the axion upconversion and axion downconversion
processes. The approach demonstrates phase sensitivity with an ability to
detect axion phase with respect to externally pumped signals. Axion signal to
phase spectral density conversion is calculated for open and closed loop
detection schemes. The fundamental limits of the proposed approach come from
the precision of frequency and environment control electronics, rather than
fundamental thermal fluctuations allowing for table-top experiments approaching
state-of-the-art cryogenic axion searches in sensitivity. Practical
realisations are considered, including a TE-TM mode pair in a cylindrical
cavity resonator and two orthogonally polarised modes in a Fabry-P{\'e}rot
cavity.
