Do stars have "radio photospheres"? Are they different from their optical photospheres?
Stars certainly do have radio emission from their photospheres, since blackbodies emit at all wavelengths. But that’s not usually what is detected, because it’s so faint.  Doing some simple numbers, emission from a star like the Sun peaks at a wavelength of about 500 nm (= $5 \times 10^{-7}$ m), and the long-wavelength side of the Planck function, in the Rayleigh-Jeans approximation, goes as $\lambda^{-4}$, so at a wavelength of 5 cm (= $5 \times 10^{-2}$ m) the emission will be $10^{20}$ times fainter.  With nearby or very luminous stars it is possible to detect this in some cases (e.g. with ALMA which is both very sensitive at operates at somewhat shorter wavelengths), but more typically the radio emission detected is from other processes like synchrotron emission.
Whether the radio photosphere is at a substantially different radius depends on the opacity at that wavelength, but Reid &amp; Menten (1996) Radio Photospheres of Red Giant Stars suggests that for some giants it may be a lot bigger than the optical photosphere.
From the abstract:

[...]These observations suggest that long period variables have a “radio photosphere” at about two stellar radii, where the stellar radius is defined by line-free regions at optical wavelengths. The radio photosphere is just inside the SiO maser shell, and the limited variability of the radio emission suggests that stellar shocks are mostly damped within this region. The density and temperature of the radio photosphere are estimated to be &gt;~ 1012 cm-3 and $\approx$ 1400 K, respectively. For these physical conditions, free electrons, obtained predominantly from the ionization of potassium and sodium atoms, provide the opacity through interactions with neutral H atoms and H2 molecules.