Why does my phallus change shape?

Do you mean why does your penis become erect? It's caused by erectile tissue. "Erectile tissue" is any tissue that is capable of stiffening or engorging with blood. During sexual arousal, sexual erectile tissue experiences increased blood flow and becomes engorged with blood, enlargening and stiffening.

It's the blood distribution inside that does that

If you place your dildo far away or up close...

Hey Cupid you are strangely obsessed with your bodily dysfunctions and heart disorder and you say you are fat and have diabetes so u have to look at that and baack up and listen to yourself and your picture u are drawing here and get some help 4 real..or maybe u just wanna make us feel powerless??? u wouldn't wanna do that I know.

Maybe you in da moood, or it gets hot or coldd.