odeset choosing internal stepsize in odesolver ode23 or ode45?

I am optimizing a function with fminunc() where an ode is being solved via ode23:

tspan=[0 1 2 3 4 5 6 7 8 9 10] ; Phi0=[0 0 0 0];

[T2,PHI2]=ode23(@(t,Phi)rSeite3b(t,Phi,E,A2),tspan,Phi0);

function dPhi=rSeite3b(t,Phi,E,A2)
% Anfangswerte
A=reshape(A2(9:24),4,4);

Z0=(A2(1:4)*expm(A*t)+A2(5:8)*integral(@(t1) expm((t-t1)*A),0,t,'ArrayValued',true))*E;%
dPhi=zeros(4,1);
% System der DGL
dPhi=(Phi'*A+Z0)';

A2 is a 24-1-Vector,

E is a 4x4 MAtrix with one 1 and all other Positions 0.

function is optimized over A2 (24 variables)

My problem: Calculation is way to slow. PArticularly Z0 needs a lot of time. Since the ode-solver is being used many times, I hope to save time by setting internal step size of ode23 and having Z0 calculating less often, outside of rSeiteb() and only being passed to rSeiteb() as a vector.

I can decide via tspan how the output should look like, but this doesn't help me, since matlab uses internally many more t while calculating ode23 or ode45. I know maxStep but, I would need minStep as well.

Is there a way to manipulate internal step size of the odesolver?

Thanks