To construct the function \( g(x) \) from \( f(x) = \log_8(x) \), we first reflect the graph across the y-axis, giving us \( f(-x) = \log_8(-x) \). Then, we vertically shrink it by a factor of \( \frac{1}{5} \), resulting in \( \frac{1}{5} \log_8(-x) \), and finally, we shift the graph down by 7 units to obtain \( g(x) = \frac{1}{5} \log_8(-x) - 7 \).
Thus, the final function is: \[ g(x) = \frac{1}{5} \log_8(-x) - 7. \]