Blood in the phlegm during dengue is a warning sign, not a small thing - it usually means your platelets have dropped and the mucosa is bleeding. Some of it can be from a raw throat or bleeding gums, but I cannot assume that while dengue is active. This needs a same-day platelet count and haematocrit, not home observation.
Next Steps
Get a repeat CBC today, keep fluids high, paracetamol only and absolutely no aspirin, ibuprofen or diclofenac. Go to the nearest emergency right away if you vomit blood, pass black stools, bleed from the nose or gums, feel giddy, or urine output falls. Send me your reports on a Practo consult and I will guide you on whether you can stay home or need admission.