How to Determine if FIR has a Linear_Phase Response w/o Matlab
Real-valued and causal FIR filters have a (generalized) linear phase response if and only if their coefficients satisfy either

$$h[n]=h[N-1-n]\tag{1}$$

or

$$h[n]=-h[N-1-n]\tag{2}$$

where $N$ is the filter length (number of taps).

There are four types of linear phase FIR filters, depending on the type of symmetry (even as in $(1)$ or odd as in $(2)$), and the filter length $N$ (even or odd). They have different properties, which is explained in this more detailed answer.