Dick Johnson said in 2001:

In my opinion it is reasonably safe to ground launch a Phoebus A,B, or
C sailplane as long as the initial acceleration is not too great. The
all-moving horizontal tail on these sailplanes have more propensity to
stall than those of sailplanes equipped with conventional fixed
stabilizer/elevator configurations. When the all-moving stabilizer
stalls during an excessively high acceleration take-off, pushing the
control stick forward usually just puts the horizontal tail deeper
into its stall, and therefore it is even more ineffective.

At low airspeeds, the nose up couple produced by a strong tow rope
pull and a high sailplane CG location can easily overpower the
aerodynamic nose down capability of an elevator control system, and
that leads to an uncontrollable nose up pitch during take-off. In a
number of instances, this has lead to the sailplane stalling and
crashing; usually with fatal results. The Phoebus is not the only
sailplane that is susceptible to this fault, so be careful of high
initial tow acceleration - auto as well as winch. I have been there!
Dick Johnson