I would guess that you actually are experiencing cramping of the toes, especially if, when your toes lock up, you have a lot of pain in the affected toes. Pain and 'locking up' is basically the definitely of a cramp!
Also it is very common to have a cramp just affect one or two toes at a time and not causes symptoms in all of the toes simultaneously.
The most common cause of cramps in the toes and legs is fatigue of the muscles. For example, if you have recently started running or otherwise vigorously exercising, this would be the most likely explanation for your cramping.
Dehydration can also cause muscle cramping, mostly by affecting the levels of various important salts in the blood stream. Make sure to stay well hydrated through out the day, especially if you are exercising vigorously or sweating a lot.
Finally there are a few medical conditions which can cause cramping. One of the most common is low levels of calcium in the bloodstream, which is something that your doctor
can diagnose with simple blood tests.
I suggest that you start by making an appointment with your primary care doctor
for evaluation of this issue.