This paper proposes a new approach of the Laser Induced Phosphorescence (LIP) signal for instantaneous surface temperature measurements: the "full spectrum fitting" method. LIP is a semi-invasive optical diagnostic based on coated thermographic phosphor surfaces, emitting a temperature-dependent signal under laser irradiation. Thousands of Mg3.5FGeO5:Mn phosphorescence spectra are acquired to build a database at each kelvin in a temperature range from 100 K to 900 K with a unique set of experimental acquisition parameters. The constituted database is used to retrieve a single-shot temperature measurement using a least mean square method. A statistical study on 70,000 single-shots acquisitions shows good precision and low uncertainties with this method.