Question: How to find the location of extreme points?

I have a function (see attached file).  How can I find by Maple 
those values of beta and f for which W will have 
three consecutive local extrema between the
phi=0 and phi_0 where W=dW/dphi=0 at phi=0 and W=0 at phi_0 and W<0 for 0<abs(phi)<phi_0?

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