  Transition blazars exhibit a shift from one subclass to the next during
different flux states. It is therefore crucial to study them to understand the
underlying physics of blazars. We probe the origin of the multi-wavelength
emission from the transition blazar B2 1308+326 using 14-year-long gamma-ray
light curve from Fermi and the quasi-simultaneous data from Swift. We used the
Bayesian block algorithm to identify epochs of flaring and quiescent flux
states and modelled the broadband SEDs for these epochs. We employed the
one-zone leptonic model in which the synchrotron emission causes the low-energy
part of the SED and the high-energy part is produced by the IC emission of
external seed photons. We also investigated its multi-band variability
properties and gamma-ray flux distribution, and the correlation between optical
and gamma-ray emissions. We observed a historically bright flare from B2
1308+326 across the optical to gamma-ray bands in June and July 2022. The
highest daily averaged gamma-ray flux was (14.24$\pm$2.36) $\times$ 10$^{-7}$
ph cm$^{-2}$ s$^{-1}$ and was detected on 1 July 2022. The gamma-ray flux
distribution was found to be log-normal. The optical and gamma-ray emissions
are well correlated with zero time lag. The synchrotron peak frequency changes
from $\sim 8 \times$ 10$^{12}$ Hz (in the quiescent state) to $\sim 6 \times$
10$^{14}$ Hz (in the flaring state), together with a decrease in the Compton
dominance providing a hint that the source transitions from a LSP to an ISP.
The SEDs for these two states are well-fitted by one-zone leptonic models. The
parameters in the model fits are essentially consistent between both SEDs,
except for the Doppler-beaming factor, which changes from $\sim$15.6 to
$\sim$27 during the transition. An increase in the Doppler factor might cause
both the flare and the transition of B2 1308+326 from an LSP to an ISP blazar.
