My Paladin/Wild Mage is level 9 (6/3). She should have 4 1st and 2 2nd for paladin. And 4 1st and 2 2nd for Sorcerer. But DND beyond says I should have access to Lv3 spell slots. Is this a bug? Or am I reading the PHB wrong?
A sorcerer counts as a full spellcaster (you take all the sorcerer levels), but a Paladin counts as "half" a spellcaster (you take half the Paladin levels, rounded down). Therefore, your equivalent spellcaster level is 6. You have four 1st level, three 2nd level and three 3rd level spell slots.
For the spell known, you take your classes separately: you can know the spells of a 9th level Paladin and a 3rd level sorcerer.
My Paladin/Wild Mage is level 9 (6/3). She should have 4 1st and 2 2nd for paladin. And 4 1st and 2 2nd for Sorcerer. But DND beyond says I should have access to Lv3 spell slots. Is this a bug? Or am I reading the PHB wrong?
Sounds like you are just reading wrong section of PHB. Try here:
https://www.dndbeyond.com/sources/basic-rules/customization-options#Spellcasting
So my Lv 9 Paladin6/Wild Mage3. I use the row for Lv 9? So I can upcast my Lv 1 and 2 spells up to level 5??
A sorcerer counts as a full spellcaster (you take all the sorcerer levels), but a Paladin counts as "half" a spellcaster (you take half the Paladin levels, rounded down). Therefore, your equivalent spellcaster level is 6. You have four 1st level, three 2nd level and three 3rd level spell slots.
For the spell known, you take your classes separately: you can know the spells of a 9th level Paladin and a 3rd level sorcerer.
Didn't read closely enough. Your paladin levels only count as half, so you use the level 6 chart.