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Type I thyroplasty is widely used to improve voice production in patients affected by unilateral vocal fold paralysis. Almost two-thirds of laryngologists report using Silastic® implants to medialize the vocal fold, with implant size, shape, and location determined experientially. However, post-surgical complications arising from this procedure (extrusion, migration, resizing) necessitate revision in 4.5–16% of patients. To improve initial surgical outcomes, we have developed a subject-specific modeling tool, PhonoSim, which uses model reconstruction from MRI scans to predict the optimal implantation location. Eleven vocal fold sample sides from eight larynges of New Zealand white rabbits were randomized to two groups: PhonoSim informed (n = 6), and control (no model guidance, n = 5). Larynges were scanned ex vivo in the abducted configuration using a vertical-bore 11.7 T microimaging system, and images were used for subject-specific modeling. The PhonoSim tool simulated vocal fold adduction for multiple implant location placements to evaluate vocal fold adduction at the medial surface. The best implant placement coordinates were output for the 6 samples in the PhonoSim group. Control placements were determined by the same surgeon based on anatomical landmarks. Post-surgical MRI scans were performed for all samples to evaluate medialization in implanted vocal folds. Results show that PhonoSim-guided implantation achieved higher vocal fold medialization relative to controls (28 to 55% vs. − 29 to 39% respectively, in the glottal area reduction), suggesting that this tool has the potential to improve outcomes and revision rates for type I thyroplasty.