This article deals with an experimental determination of the relative phase angle between the shedding of vortices and motion in the case of the Aeolian vibrations of a flexible circular tube. The objective is to compare and determine if the phase value of a transient regime differs from that measured in a steady vibrating state. For each mode of vortex shedding (Von Ka´rma´n, 2S and 2P), the results show that the value of the phase angle in the unsteady and steady regimes is relatively similar if an appropriate dependency is selected: in the cases of the 2P and 2S modes of vortex shedding, this dependency is either the dimensionless amplitude or the ratio of the velocity of the structure motion to the oncoming flow velocity; in the case of the Von Ka´rma´n regime, at the onset of the instability, the usual reduced velocity is a better dependent variable. The analysis of jumps occurring in the instruments output reveals a boundary between the Von Ka´rma´n and the 2P modes of vortex shedding.