In the code below, the circle grows/shrinks repeatedly. How can I make it so it only grows once - while it 'shakes' and then stop and stay at its largest size?

float x1 = -180;       //O
float y1 = 180;
float speed = 0.05;
float angle = 0.0;

void setup(){
 size(600,400);
 noStroke();
 smooth();
 fill(255);
}
void circlePhase(float phase){  
 ellipse(x1,y1,40,40);
     x1 += 5;
 if (x1 > 280){
     x1 = 280;
     x1 += random(15);
 }
 float diameter = 30 + (sin (angle + phase) * 45);
 ellipse(x1, y1, diameter, diameter);
}  

void draw(){
 background(0);
 frameRate(30);
 circlePhase(0.0);
 angle += speed;}