= Solution
The null momentum equation gives $p^i=C^i e^{-\Phi}$, with a constant <null vector> $C^i$. Since the tangent is parallel to $p^i$, every spatial direction ratio is constant:
$$
\frac{dx^a}{dx^0}=\frac{p^a}{p^0}=\frac{C^a}{C^0},\qquad a=1,2,3.
$$
The changing potential changes the scale of the <four-momentum>, not its direction. <Photon> paths are therefore straight lines in the background <Minkowski spacetime>, up to reparametrization. This is also consistent with <conformal preservation of null geodesic paths>: the particle motion law can be expressed through a conformally flat metric, which cannot change the unparametrized null trajectories of the background.
Hence \b[no: the theory predicts zero solar light deflection], in disagreement with the observed nonzero bending of light. For comparison, the leading <Schwarzschild light deflection> is $4GM/(bc^2)$ at impact parameter $b$. The scalar theory's nonzero <gravitational redshift> does not rescue this failed directional prediction.
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