The ion phase in the internal beam of the Birmingham cyclotron at distances from the ion source from 8 mm up to 69 cm has been determined by measurements of the target current waveform. The equipment consisted of a screened target and a specially built oscilloscope based on the sampling technique. The results obtained are discussed and compared with theory.Ions are grouped in phase at early stages of acceleration over approximately 20 electrical degrees, which is about 5 times larger than predicted by the uniform electric field approximation. At later stages the measured phase changes are in good agreement with Rose's equation.