Nanocolloidal lasers have a potential as inexpensive high-power light sources using non-toxic and non-degradable liquid gain media. However, due to their large core and, as a result, multimode operation they have an issue of strong noise produced by mode competition. An advanced solution would be the selection of active modes down to a single-mode using the parity-time (PT) symmetry approach that originates from the analogy between the Schrödinger wave function equation in quantum mechanics and the wave propagation equation in optics. The PT symmetry lasing will be implemented when spatially inhomogeneous pumping of the nanocolloid generates gain in pumped regions equal in magnitude to the loss in the regions without pumping. When pump energy increases, PT symmetry break occurs and the laser modes split in the active modes amplified in the cavity and those that decay. The goal is to achieve a single-mode nanocolloid laser. On the way to the goal a nanocolloidal capillary optical amplifier was built using highly efficient phosphor NaYF4: Yb3+ , Er3+ emitting at 1550-nm wavelength being pumped with a 980-nm laser diode. The amplifier was configured as a 4-cm long capillary tube made of silica filled with a colloid of 160-nm phosphor nanoparticles in a high- index fluid. Uneven pumping from the side modulated the gain of the amplifier. When the amplifier was to converted into a laser with linear resonator, uneven side pumping produced a variation of the spontaneous emission that could be interpreted as a PT symmetry related mode competition. This potentially could lead to the reduction of active modes and eventually to a single mode operation.