"Mother of all" is an idiom used to emphasize the magnitude, significance, or scale of something. While this phrase is commonly employed, it is always good to have alternatives to keep our language versatile and engaging. One of the substitute phrases can be "the ultimate" or "the granddaddy" to convey the same sense of importance. Another option is "the epitome", which means the perfect example or embodiment of something. Moreover, "the pinnacle" and "the apex" can be used to suggest the highest point or climax. Lastly, "the paramount" or "the supreme" can effectively convey the idea of something being the most significant or powerful.