We have screened 18 Phoma spp. for the mycosynthesis of silver nanoparticles (AgNPs). Out of 18, 17 Phoma spp. demonstrated mycosynthesis of AgNPs, which were characterized by UV–vis spectrophotometry, Fourier transform infrared, X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoparticle tracking and analysis system, and zeta potential measurement. SEM and TEM analysis showed the mycosynthesis of polydispersed spherical AgNPs, with the exception by P. sorghina (MTCC-2096), which revealed the fabrication of silver nanorods. The effect of pH, temperature, silver nitrate, fungal filtrate, and light intensity was studied to understand the mechanism of mycosynthesis of AgNPs by P. sorghina. The involvement of protein was found during the mycosynthesis but the process failed to follow the Michaelis–Menton kinetics of the enzyme-catalyzed reaction. A three-step hypothetical mechanism, that is, activation, nucleation, and reduction, for the mycosynthesis of silver nanorods is proposed. The present study will be useful for the stable and rapid mycosynthesis of AgNPs. The extracellular process involved in synthesis of AgNPs was found to be rapid, simple, easy, and ecofriendly.