Using the program, we can find the following pairs of $n$.
$\lambda,~\text{nm}$ $\Phi=60^\circ$ $\Phi=50^\circ$ $n_1$ $n_2$ $n_1$ $n_2$ 378 1.4732 2.0771 1.0129 1.4726 406 1.4698 2.0833 1.0144 1.4691 434 1.4671 2.0880 1.0153 1.4667 466 1.4646 2.0926 1.0162 1.4645 499 1.4624 2.0966 1.0171 1.4624 535 1.4606 2.0999 1.0179 1.4605 573 1.4590 2.1029 1.0186 1.4589 614 1.4578 2.1051 1.0191 1.4577 658 1.4566 2.1073 1.0197 1.4561 706 1.4549 2.1104 1.0202 1.4551 756 1.4537 2.1127 1.0206 1.4541 810 1.4526 2.1149 1.0210 1.4532
As you can see the $n_1$ for $\Phi=60^\circ$ is approximately equal to the $n_2$ for $\Phi=50^\circ$. Let's use their average as the answer.
Let's plot $n$ vs. $1/\lambda^2$, so that $A$ is an intercept and $B$ is a slope.