Quasi-2D perovskite materials have great potential for achieving high-performance blue perovskite light-emitting diodes (PeLEDs). Major challenges lie in the need to minimize the energy level mismatch between the blue-emitting and the charge-transport materials for better carrier injection, and to suppress low-dimensional phases in quasi-2D systems for improved radiation recombination. Here, this work introduces a subtly functionalized compound, methoxylated phenethylammonium bromide (y-MeO-PEABr), into the sky-blue quasi-2D perovskite. This approach induces an upward shift of the energy levels of the perovskite and reduces the holes injection barrier, thereby achieving a better charge balance. In addition, the introduction of large y-MeO-PEA cations effectively suppresses the formation of undesirable phases in quasi-2D perovskites, leading to a more concentrated phase distribution and accelerated energy transfer. Specifically, the sky-blue quasi-2D PeLED based on 2-MeO-PEABr exhibits optimal device performance, obtaining a maximum external quantum efficiency of 10.85% at 486 nm. This work suggests that this method may provide a guide for designing novel organic spacer cations to obtain high-performance blue quasi-2D PeLEDs.