Geopolymers are an inorganic cementitious material that is gaining attention for its exceptional mechanical qualities, strong thermal resistance, and low dielectric properties. However, the brittle failure and low ductility of geopolymers limit their use in load-bearing or structural applications. To overcome this challenge, the present work focused on improving the physico-mechanical, water, and thermal resistance properties of geopolymers by reinforcing untreated and alkali-treated (5, 10, and 15% concentrations) Phoenixsp. fibers. The outcomes revealed that the incorporation of Phoenixsp. fibers improved the performance of the geopolymer. In particular, the geopolymer reinforced with 10% alkali-treated fibers showed substantial improvement in their characteristics. The microstructural investigation demonstrated that the treated fibers formed a good interfacial bond with the geopolymers. In addition, load–deflection tests were conducted to examine the viability of the Phoenixsp. fiber–based geopolymer composites for structural applications. The findings of this study indicate that using alkali Phoenixsp. fibers as a fibrous material in the manufacturing of ecologically friendly and durable geopolymer concrete has a promising future in the construction sector.