Digital beamforming and phase shift stage insertion
In a first analysis, it does not matter where the phase shifting is inserted, as long as the mixing stage is linear.

Indeed, shifting a temporal signal is equivalent to multiplying it with a complex number integration the phase shift $\theta$ :


Unshifted signal : $s(t)$
$\theta$ phase shifted signal : $s'(t) = s(t).e^{j\theta}$
$f_0$ carrier mixed unshifted signal : $s_c(t) = s(t).c(t) = s(t).e^{2j\pi f_0.t}$
$f_0$ carrier mixed $\theta$ shifted signal : $s'_c(t) =s(t).e^{2j\pi f_0.t}.e^{j\theta}$ = $s(t).c'(t)$ 


where $c'(t) = e^{j(2\pi f_0.t+\theta)}$ is the shifted carrier.

In the end phase shifting the signal to be modulated is equivalent to phase shifting after carrier modulation.