I present our recent results of an extensive investigation of the flux-tube spectrum and what these teach us about the axion on the worldsheet of the confining string. Namely, we analyze confining string spectra for SU(3), SU(5) and SU(6) using the lattice machinery. Using the thermodynamic Bethe ansatz (TBA) method, incorporating certain approximations, we validate that a significant portion of the low-lying energy states described by different sets of quantum number can be effectively characterized by the low energy effective theory of a long string described by two Goldstone bosons called phonons, along with a massive pseudoscalar called the worldsheet axion. Moreover, we are able to describe the axion-axion and axion-phonon interactions using TTbar deformation leading to an additional tower of states!