Rolling <anything>
Roll, and then
finish} the <anything> call.
All of the "ing" calls (Flowing, Rolling, etc.) apply some action
to the preceding call, and then let that action replace the first part
of the "anything" call.
\begin{displaydance}
\phfour{b1n,g1s,g2n,b2s} & \phBB{g1s,b2n,b1s,g2n} & \phBB{g1w,b2e,b1w,g2e} & \phfour{g2s,b1n,b2s,g1n} \cr
\cbox{before Recycle} & \cbox{before Rolling\\Contour the Line} & \cbox{after Roll} & finished \\
\end{displaydance