How to crate only 5 plots out of the 20000 iterations?

This is my code and i am trying to plot using imagesc to just show a plot at 0, 5, 10, 15, and 20s only althought there are so many iterations but they all are useless to me, how can I do that efficently and for all number of iterations?

% Five Point Stencils:
        % Common constants:
        a = 1; b = 1; gamma = 1; D = 3; nROWS = 150; nCOLS = 100; stencil = 5;
        % The h spacing is a constant:
        h = 1; 
        % Initial and final time conditions.
        t0 = 0; tf = 20; dt = 1e-3;
        % time vector and time iteration size.
        t = t0:dt:tf;
        mt = length(t);
        % phi is a random nROWS x nCOLS matrix that contains only 1 & -1:
        phi = floor(randsrc(nROWS,nCOLS,[-1,1 ; 0.5,0.5]));
        % newphi matirx:
        newphi = zeros(nROWS,nCOLS);
        % Plotting initial:
        figure (1)
        imagesc(phi)
        % Material A is 1 and Material B is -1
        colorbar
        caxis([-1 1])
        title(['1st Order Euler Field Distribution at stencil = ' num2str(stencil) ', dt = ' num2str(dt) 's, and t = ' num2str(t0) 's.'],'FontSize',18)
        set(gca,'LineWidth',1,'FontSize',8)
        axis equal
        for k = 1:mt-1
            % Eqn 4:
            v1 = Laplacian_2D(phi,h,stencil);
            v2 = (b^4 * phi.^3 - a * b^2 * phi) - gamma * v1;
            v3 = D * Laplacian_2D(v2,h,stencil);
            newphi = phi + dt * v3;
            phi = newphi;
            if k == 5000
                % Plotting at 5 seconds:
                figure (2)
                imagesc(phi)
                colorbar
                caxis([-1 1])
                title(['1st Order Euler Field Distribution at stencil = ' num2str(stencil) ', dt = ' num2str(dt) 's, and t = ' num2str(5) 's.'],'FontSize',18)
                set(gca,'LineWidth',1,'FontSize',8)
                axis equal
            elseif k == 10000
                % Plotting at 10 seconds:
                figure (3)
                imagesc(phi)
                colorbar
                caxis([-1 1])
                title(['1st Order Euler Field Distribution at stencil = ' num2str(stencil) ', dt = ' num2str(dt) 's, and t = ' num2str(10) 's.'],'FontSize',18)
                set(gca,'LineWidth',1,'FontSize',8)
                axis equal
            elseif k == 15000
                % Plotting at 15 seconds:
                figure (4)
                imagesc(phi)
                colorbar
                caxis([-1 1])
                title(['1st Order Euler Field Distribution at stencil = ' num2str(stencil) ', dt = ' num2str(dt) 's, and t = ' num2str(15) 's.'],'FontSize',18)
                set(gca,'LineWidth',1,'FontSize',8)
                axis equal
            elseif k == 20000
                % Plotting at 20 seconds:
                figure (5)
                imagesc(phi)
                colorbar
                caxis([-1 1])
                title(['1st Order Euler Field Distribution at stencil = ' num2str(stencil) ', dt = ' num2str(dt) 's, and t = ' num2str(20) 's.'],'FontSize',18)
                set(gca,'LineWidth',1,'FontSize',8)
                axis equal
            end
        end

Answer 1

[the cyclist]

Use

if mod(k,5000)==0
    ...
end

and just

figure

or

figure(k/5000)

Just using the figure command (without any argument) will open a new figure, with the next consecutive available number.