If spacetime is “foamy” travel along a lightpath must be subject to continual, random distance fluctuations ± δ l proportional to Planck length lP ~ 10−35 m (Lieu & Hillman 2003). Although each “kick” by itself is tiny, these may accumulate. Accounting for redshifted (bluer) emitted photons, over a cosmological distance L = (1+z)LC for co-moving distance LC, the resultant phase perturbations Δ φ = 2π δ l/λ at observed wavelength λ could grow independently of telescope diameter D to a maximum of Δφmax=(1+z)Δφ0 (Steinbring 2007) where Δφ0=2π a0 (lPα/λ)L1 - α follows Ng et al. (2003). Here a0 ~ 1 and α specifies the quantum-gravity model: 1/2 implies a random walk and 2/3 is consistent with the holographic principle; a vanishingly small ΔφP=Δφmax/[(1 + z) a0 (L/lP)1 - α]=2π lP/λ is approached when α=1.