@Birhen_ng_Guadalupe - Ma'am tama po si lock, may residency test po and kahit na naginitial entry ka na sa Au kung hindi mo nameet ang residency requirement e hindi ka magiging taxable sa Au for income earned in Sg. Also, related sa post ni psychoboy, may tax treaty ang Au and SG wherein ang personal/professional services income (remuneration) is taxable only on the place where the service is rendered. I'm not sure kung kelangan pa itong ideclare as income subject to final tax sa Au tax filing. Baka may makapagcomment regarding this.
Regarding Loki's comment, tama po na may double tax treaty ang Au and Phil and same with Sg ang income from remuneration is only taxable in the place where the service is rendered. But this is subject to some exceptions, meaning the remuneration income in the Phil can still be taxable in Au subject to some factors.
I haven't tried filing an Au individual tax return pero I understand that Au tax residents are required to declare all income derived from within and outside of Au. If the Au tax resident suffered income tax from its income derived from outside of Au, then the tax resident shall be able to claim tax credit (tax offset) for the said taxes paid, meaning the total Au income tax payable may be reduced by claiming the tax credits for the taxes paid in foreign jurisdictions.
Hope this helped in some way. 🙂