Hi & welcome! Agree, looks like aphids. You can pinch the affected tips off, and moving the pot might help, if that's an option. Ants might have put the aphids on the plants to farm their honeydew. I've never had a problem getting rid of aphids by making minor efforts to trim the affected plant parts (& rinsing other kinds of plants that might not grow back as fast as Portulaca.) Dabbing at them with a Q-tip damp with rubbing alcohol should also kill the ones you touch and help clean up the tips if you don't want to trim them. Aphids are not a permanent malady like scale or mealybug if efforts are made to thwart them. I think the white things are discarded, shedded skins. If they don't move, that would be evidence toward that.
