When it comes to synonyms for "phone up," several options can be used to add some variety to your communication. One option is to say "call up," which refers to placing a phone call. Another option is to use "ring up," which can be used instead of phone up or call up. If you want to convey a sense of urgency, you can also use "dial up" or "telephone immediately." Further synonyms include "reach out," "contact," or simply "get in touch." By using these alternate options, you can add some variety and precision to your language, making your communication more effective and engaging.