You could technically do it the same way, e.g.
hw = phased.FMCWWaveform('SweepBandwidth',1e7,'SampleRate',2e7,...
'SweepDirection','Triangle','NumSweeps',2);
x = step(hw);
ambgfun(x,hw.SampleRate,1/(2*hw.SweepTime))
As a side note, there is also something called periodic ambiguity function which is designed for cw signals, but Phased Array System Toolbox currently doesn't offer that.